The present invention relates to a heat-sensitive lithographic printing plate precursor which requires no development. More specifically, the present invention relates to a heat-sensitive lithographic printing plate precursor, whose sensitivity is improved, capable of image-recording by infrared ray laser beam scanning exposure based on digital signals, and capable of being directly mounted on a printing machine (i.e., a printing press) without undergoing conventional development processing after image recording to effect printing.
Various methods of lithographic printing plate precursors capable of being directly mounted on a printing machine without development processing after exposure and effecting printing have been suggested. One promising method is a method of utilizing ablation, wherein a lithographic printing plate precursor is subjected to exposure with solid state high output infrared ray laser beams such as a semi-conductor laser or a YAG laser to make the exposed area generate heat by a compound capable of converting light into heat, to thereby cause cracking evaporation.
That is, this is a method of providing a hydrophilic layer on a lipophilic and ink-receptive surface or on a substrate having a lipophilic and ink-receptive layer and removing the hydrophilic layer by ablation.
For example, a heat-sensitive lithographic printing plate precursor comprising a substrate having coated thereon an ink-receptive layer containing a compound capable of converting light into heat which converts light to heat, and a hydrophilic layer coated thereon containing a colloidal particle oxide or a hydroxide of, e.g., silicon, is disclosed in WO 98/40212.
It is suggested in WO 99/19143 to add a compound capable of converting light into heat not only to an ink-receptive layer but also to a hydrophilic layer. Further, it is disclosed in WO 99/19144 to provide a heat-insulating layer comprising a thermoplastic polymer between a support and a hydrophilic layer.
The purpose of these techniques is, e.g., in the case of WO 98/40212, to improve the problem of the reduction of sensitivity of a heat-sensitive lithographic printing plate precursor resulting by the reduction of the ratio of heat to be used in ablation due to the diffusion of the generated heat to the substrate since a compound capable of converting light into heat is contained in a layer adjacent to a substrate.
However, in particular in the case of using an aluminum plate having high heat conductivity as a support, the influence of heat diffusion to a support is high and the sensitivity of a heat-sensitive lithographic printing plate precursor could not be improved sufficiently satisfactorily even according to the improved techniques disclosed in the above patent specifications.
Accordingly, an object of the present invention is to solve the above problem. That is, an object of the present invention is to provide a heat-sensitive lithographic printing plate precursor having an aluminum support which can be directly mounted on a printing machine without development processing after exposure to effect printing and is improved in sensitivity.
As a result of eager investigations, the present inventors have found that when an aluminum plate is used as a support, the heat diffusion to a support can be reduced by providing a so-called heat-insulating aerial layer on the surface of the support to seal the pores on the anodic oxide film of the support, thus the above object can be attained.
That is, the present invention has been accomplished by the following means.
(1) A heat-sensitive lithographic printing plate precursor which comprises an aluminum support having provided thereon an ink-receptive layer and a hydrophilic layer containing a colloidal particle oxide or hydroxide of at least one element selected from the group consisting of beryllium, magnesium, aluminum, silicon, titanium, boron, germanium, tin, zirconium, iron, vanadium, antimony and transition metals, wherein at least one layer of the ink-receptive layer and the hydrophilic layer contains a compound capable of converting light into heat, the aluminum support has an anodic oxide film in an amount of 2 g/m2 or more, and the anodic oxide film has been subjected to sealing treatment at a sealing rate of 50% or more.
(2) The heat-sensitive lithographic printing plate precursor which comprises an aluminum support having provided thereon an ink-receptive layer and the hydrophilic layer as described in the above item (1), wherein a water-soluble overcoat layer is further provided over the aluminum support; and at least one layer of the ink-receptive layer, the hydrophilic layer and the water-soluble overcoat layer contains a compound capable of converting light into heat, the aluminum support has an anodic oxide film in an amount of 2 g/m2 or more, and the anodic oxide film has been subjected to sealing treatment at a sealing rate of 50% or more.